That is indeed a nifty use case, but also kind of a special case in which a serialized AST is the required output of your program. For the general case where th

That is indeed a nifty use case, but also kind of a special case in which a serialized AST is the required output of your program. For the general case where the DSL is just a sexy API, I wouldn't recommend building a parse tree. EDIT: Actually, for your case I don't think I would use sexps. I would write some primitive validators in Ruby that can also generate equivalent JavaScript code, then use those to build higher order validators in Ruby alone. Compare that to maintaining complete validator engines in two different languages.